The human sex chromosomes have evolved a complex genomic architecture consisting of a plethora of highly homogenous palindromic sequences harboring testis expressed genes. The high level of nucleotide sequence identity between palindrome arms is believed to be the result of palindrome arm-to-arm recombination. Recombination between Y-specific palindrome arms can cause large deletions of critical testis genes resulting in male infertility. The recent mouse sex chromosome sequences reveal that they also contain large palindromes, thus, providing an excellent model system to study sex chromosome palindromes. Aims 1+2 investigates whether arm-to-arm recombination, also known as gene conversion, is acting on the mouse Y-specific palindromes. Detection of gene conversion within the mouse Y-palindromes would explain the high levels of nucleotide sequence identity between palindrome arms. Aim 3 examines the expression patterns of mouse sex chromosome palindrome associated genes to elucidate palindromes functions during spermatogenesis. Characterization of sex-chromosome palindromes and their associated genes will be of relevance to understanding the mechanisms of gene conversion and male fertility. [unreadable] [unreadable] [unreadable]